铜绿微囊藻气囊蛋白的结构和功能研究

Microcystis aeruginosa was investigated and identified as a planktonic unicellular cyanobacterium which is responsible for algal bloom in the freshwater environments. In Microcystis cells, an abundant production of intracellular structures, the gas vesicle, an inert, hollow and gas-filled structure, formed solely from proteins, provides cells with buoyancy and regulates their vertical distribution in natural waters. Cyanobacteria could float taxis toward air-liquid interfaces of water environments, positioning themselves at a depth with optimal light and oxygen supply for better growth, subsequent niche colonization and water-bloom formation. However, the fine structure of gas vesicle and its biosynthesis/degradation mechanisms are still unclear. To determine three dimensional structures of gas vesicle proteins and remodeling the integral hollow structure, we are committed to solve structures of Gvp proteins from Microcystis aeruginosa PCC 7806 using X-ray crystallography. Moreover, in combination with high-resolution cryo-electron microscopy, we will investigate the localization of individual Gvp proteins by immunoblotting and immunogold labeling-based tomography. These findings will provide insights into structural characteristics of gas vesicle and the rational control of algal bloom.

铜绿微囊藻是一种单细胞浮游蓝藻，能大量产生气囊，营养丰富时在淡水水体表面聚集暴发水华。气囊是一种完全由蛋白质组成的中空、充满气体的惰性结构。气囊为藻细胞提供浮力，使其自行调节在自然水体中的垂直位置，漂浮到氧气和光照都适宜的位置以利于自身生长和生境殖民化。气囊不仅是铜绿微囊藻能成为优势藻种的重要原因之一，也在水华的暴发过程中起到了调节作用。然而，人们至今尚未弄清气囊的结构及其合成降解机制。为了探究气囊合成相关蛋白的三维结构，进一步重构气囊这一中空结构的三维面貌，我们以铜绿微囊藻Microcystis aeruginosa PCC 7806中的气囊合成相关的一组Gvp蛋白为研究对象，利用X射线晶体学手段解析各个气囊蛋白的结构，并联合运用高分辨率冷冻电镜，蛋白质免疫印迹法和胶体金标记等方法来分析各结构蛋白的具体定位。该项目将解析气囊原子分辨率水平上的三维结构，对治理水华暴发有一定理论指导意义。

蓝藻水华导致严重的经济和社会问题。形成水华的主要优势种类的蓝藻都具有气囊。气囊能通过改变细胞密度，为藻细胞提供浮力，调节蓝藻自身在水体中的位置以利于生长繁殖和生境殖民化。在本研究中，我们解析了PCC7120气囊蛋白GvpF的结构，测定了GvpN的酶动力学参数，并在大肠杆菌中组装了完整的PCC7120气囊。通过电镜观察了天然纯化的PCC7806气囊、鱼腥藻气囊和体外表达的PCC7120气囊，并获得了PCC7806的气囊数据，有望解析气囊整体结构。另外,我们还证实了鱼腥藻气囊在大鼠肝内的超声造影功能，体现了气囊潜在的临床应用价值。